CVE-2026-74496: fou: Fix use-after-free in fou_create()

CVE-2026-74496: fou: Fix use-after-free in fou_create()

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

fou: Fix use-after-free in fou_create()

fou_create() publishes struct fou through sk_user_data before adding the
new FOU port to the per-netns list.  If fou_add_to_port_list() fails,
the error path frees fou while it is still reachable through
sk_user_data.  A concurrent receive can then dereference the freed
object in fou_from_sock().

This ordering issue was previously noted in the linked discussion.

The failure is reachable when local port 0 is requested.  Each socket
binds to a different ephemeral port, but fou_cfg_cmp() compares the
requested port 0 and reports -EALREADY once an entry already exists.

Release the tunnel socket before freeing fou so sk_user_data is cleared
first, and defer reclamation with kfree_rcu() to protect concurrent RCU
readers.  This matches the lifetime handling in fou_release().

The Linux kernel CVE team has assigned CVE-2026-74496 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 3.18 with commit 23461551c00628c3f3fe9cf837bf53cf8f212b63 and fixed in 7.1.8 with commit a28d8903bfe76089ea4bbdbff9976965f9ef8107
	Issue introduced in 3.18 with commit 23461551c00628c3f3fe9cf837bf53cf8f212b63 and fixed in 7.2-rc6 with commit b14361aca6350ff7907b0e9903c7b94dc7d5d4a0

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-74496
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	net/ipv4/fou_core.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/a28d8903bfe76089ea4bbdbff9976965f9ef8107
	https://git.kernel.org/stable/c/b14361aca6350ff7907b0e9903c7b94dc7d5d4a0